The present invention relates to a suction system, in particular to a suction system for use in a method of lining the internal surface of an existing pipe buried under ground.
There has been known a no-excavation underground pipe lining method in which the internal surface of an existing underground gas pipe, water pipe, etc. are lined with a resin without the necessity of any trenching or excavation.
Usually, a gas service pipe is buried under ground branching from a gas main and extending to a user's house. In the method called no-excavation underground pipe lining, there are substantially two steps involved. In the first step, an injection system is employed to produce a pressurized liquid to introduce a necessary amount of resin into the service pipe through an open end thereof and to move the resin through the pipe until the front end of the resin plug flow reaches an inner end (a position branching from a gas main) of the pipe. In the second step, a suction system is employed to produce a suction force to suck back the liquid injected in the pipe so as to cause the resin to move back from the inner end to line the internal surface of the pipe with the resin.
A conventional suction system for use in the above-described method, usually includes (a) a pig receiving device to be attached to an open end of the pipe for receiving from the pipe various pigs used in lining treatment, (b) a liquid receiving tank connected with the pig receiving device for receiving liquid flowing back from the pipe, (c) a suction pump connected with the liquid receiving tank for producing a suction force on the liquid, various pigs and resin introduced in the pipe, to cause a backward movement of the resin so as to line the internal surface of the pipe with the back-moving resin.
However, with the use of the conventional suction system as described above, it is difficult to confirm whether the pigs introduced in the pipe and used in the lining treatment have returned or not. In particular, since it is not easy to confirm whether all the used pigs have been recovered or not, it is difficult to stop the operation of the suction pump even if the last pig has been recovered in the pig receiving device. As a result, the suction pump is often stopped too late, so that there will be too much of a gas to be sucked out of the pipe, resulting a waste of the gas.
Further, with the use of the conventional suction system as described above, it is difficult to control the suction force, resulting a problem that the in situ lining speed can not be controlled, hence it is almost impossible to obtain a resin lining layer having a desired thickness
Moreover, with the use of the conventional suction system as described above, it is difficult to prevent liquid drops from entering the suction pump, resulting in damage to the suction pump.